Electrolysis processes, for instance sulfate-based electrowinning of metals such as copper, typically take place in an electrolytic cell that contains a number of anodes and a number of cathodes arranged in an alternating manner. In the sulfate-based electrowinning process, an anode made of lead alloy or an anode with an electrocatalytically active coating and a cathode made of stainless steel are immersed in an electrolyte bath containing a solution comprising e.g. copper sulfate and sulfuric acid. An electrical current from the anode to the cathode induces an electro-chemical reaction, wherein copper is deposited on the surface of the cathode. At the same time, oxygen gas is generated on the anode. The oxygen generated forms very small bubbles on the anode surface. These bubbles subsequently rise to the surface of the electrolyte containing sulfuric acid, burst and release a fine aerosol or mist of electrolyte into the atmosphere above the electrolyte. This aerosol or mist, referred to as acid mist, typically has a similar composition as the electrolyte, i.e. contains sulphuric acid and metal salts, and has a number of harmful side effects: it is harmful to personnel working in the tankhouse and causes corrosion when deposited on surfaces in the tankhouse. The acid mist is typically composed of liquid particles or droplets of approx. 1-100 μm in diameter in suspension.
Several techniques are available for reducing acid mist in tankhouses. These include chemicals such as surfactants (e.g. FC-1100), mechanical barriers such as layers of spheres, beads and the like, improved ventilation (e.g. cross-flow) and hoods and cell covers above the cells to remove acid mist. One example of a tank cover apparatus for reducing acid mist is described in U.S. Pat. No. 5,470,445. U.S. Pat. No. 4,668,353 describes clips and masking devices that restrict the electrolyte surface area through which bubbles can pass into the atmosphere.
These techniques however have drawbacks and may be impractical to use. Hoods and cell covers are effective in removing acid mist, but they do not collect acid mist if not in place, for instance at the time cathodes are being harvested. Hoods and the scrubbing systems associated consume water and energy. Chemicals are an additional expense and they do not provide 100% reduction for acid mist. Further, it would be desirable to be able to reduce the amount of acid mist to a minimum.